Hopefully they'll be cross compatible with another browser's existing library. Namely Chrome's as FF's is a clusterfuck of plop. Not that they can because of the different architecture, but one can dream.

Opera 11 is great, and I haven't even started fiddling with extensions yet!

My only complaint so far is that the mouse gestures* seem to require more travel to trigger. They used to work with when you moved the mouse only a few pixels, but it seems to want approaching 50 pixels worth of movement before it does anything now. I'm sure I'll get used to it in time, but I did like how utterly effortless they were before.

*the new visual guide is a pretty neat way to get people started on them

edit: actually, the mouse gesture thing is starting to annoy me, as I keep having to redo gestures slightly bigger than I used to do them. Grrrrr.